222 LUTHER BURBANK 



genera representing different branches which 

 may diverge in opposite directions, and only 

 come together at the trunk. 



Then, too, there is a time element involved. 



Species that are closely similar in character and 

 appearance are those that have branched from 

 the ancestral stem in relatively recent epochs; 

 species more distinct trace their cousinship 

 through remoter lines; and forms so widely 

 diverse as to be placed in different orders have 

 been separated for still longer periods. And we 

 must suppose that in each generation the new 

 forms have taken on a modicum of new traits, 

 and have tended to fix the divergence of earlier 

 traits through which they attained specific dif- 

 ference. 



In due course, then, it comes to pass that a 

 given form has branched so widely from its 

 cousins that the harmony of purpose, so to 

 speak, once obtained between them no longer 

 obtains. 



The racial memory as to their common 

 ancestry has become blurred, if the phrase be 

 permitted, and each species has become so fixed 

 in its own manner of life that no compromise 

 between them would be possible. 



And so we find that it becomes increasingly 

 difficult to cross species that are obviously widely 



